Here are some better photos of the rear of the cylinder so you can see how it is relieved for the clips. Shown are the fullmoon and 1/3 moon clips that came with the Governor. The halfmoon clips that I shot belonged to a friend that was with me and they looked like a fullmoon clip cut in half, not the traditional 1917 type. He said he bought them at a gunshow in Crown Point, Ind. I don't have those clips so I photoshopped a full moon to show you what they look like. If you find any that look like this they will work in the Governor. Another thing I read in the owners manual is that you cannot use Auto Rim 45 ammunition in it. I think S&W had to do some really tight tolerances with the relieving the rear of the cylinder as to reliably allow the use of the clips and 45 Colt cartridges.

The purpose Smith and Wesson had in mind when including the ACP round into the design was to allow the owner/shooter a very common and fairly inexpensive cartridge option, so that one may practice and become proficient with their weapon economically.